Gas turbines, especially aircraft engines, have at least one rotor equipped with rotating runner or rotor blades especially in the area of a compressor as well as a turbine, whereby the rotor blades are increasingly embodied as an integral component of the rotor. Integral bladed rotors are also designated as “blisk” (bladed disk) or “bling” (bladed ring). Generally, through-going bored holes, extending in the radial direction, for fluids, for example oil, are generally integrated in such rotors. Such through-going bored holes are also designated as “bleed holes” and represent hollow spaces or cavities with small cross-sectional areas. Other bored holes extend in the axial direction and often serve for the screwing connection, whereby these bored holes similarly represent highly loaded zones or areas of compressor and turbine. Further cavities with small-cross sectional areas are, for example, located between neighboring rotor disks of a gas turbine rotor. During the operation of a gas turbine, especially the rotors thereof are subject to high demands. In order to reduce the wear rate, the rotors are densified or hardened by special surface treating or processing methods. In that regard, it is of significance to densify or harden also the surfaces of the above described cavities with small cross-sectional areas and the associated transition radii.
For the hardening of surfaces, the shot peening or shot blasting is usually used according to the state of the art, whereby the shot balls are accelerated with the aid of an airstream or a centrifuge. If, for example, the surfaces of through-going bored holes are to be hardened with the aid of shot balls accelerated by an airstream or a centrifuge, the problem arises, that especially corners or transition areas of the through-going bored holes between a surface of the rotor and an inner surface of the through-going bored holes are subjected to a strong plastic material deformation, whereby the ductility of the material in the area of the through-going bored holes can be reduced and thus disadvantageously influenced. The methods for the surface blasting known from the state of the art are thus suitable only with great limitations for the treatment of cavities with especially tight cross-sectional areas.